This is potentially exciting as I regard electric car technology as very important. It means that the fuel doesn't have to be petroleum, and results in quiet cars, which would greatly improve the quality of life in urban areas and for those living near highways. The electricity might be generated by fossil fuel but could be that generated uselessly at night, and it might be renewable energy.
Let's look at Tesla's patent specifications. Figures stated are as of today, 14 June 2014: there are lots more now.
It has 373 US patent applications, where an attempt has been made to secure a patent, and 168 granted US patents. Of these, 76 and 21 respectively were published in 2013-2014. There are also 8 US design patents, for the look rather than function in the listed utility patents (that list is from Google Patents). For example, D683268:
These utility patents include Dual mode range extended electric vehicle;and Charge state indicator for an electric vehicle, which is illustrated below.
So why do it ? If Tesla can expand the market for electric cars there will be more charging stations and hence more people will be tempted to buy one. Also, inventions based on Tesla's work will presumably be compatible and hence can be incorporated into future work by Tesla.